Cooling agents have been used in a number of different formulations, such as hard confectionary products or oral gums, to provide a pleasant taste and a cooling sensation. For example, compounds such as menthol or peppermint oil have been used in either as part of the formulation or as part of a coating in order to provide the user with a cooling sensation.
Cooling agents have also been used in pharmaceutical formulations to enhance the physiological and/or perceived benefits, such as speed or duration of relief. Such agents are commonly used in non-prescription cough medicines.
Sore throats are generally treated using pharmaceutical lozenges containing a therapeutically effective amount of an active compound. Suitably, the lozenge is sucked by a patient in need of such treatment and the active is released in the oral cavity and delivered to the surface of the sore throat (i.e., mucous membrane).
Some of the actives which are used to relieve the symptoms associated with a sore throat can cause an unpleasant burning sensation at the back of the mouth when retained in the mouth, e.g., a non-steroidal anti-inflammatory drug (NSAID). This is unacceptable to the patient being treated. Consequently, pharmaceutical lozenges containing actives such as an NSAID have been devised where the lozenge formed therefrom relieves the symptoms of a sore throat but the patient does not experience an unacceptable burning sensation.
Cooling agents have also been used with sweeteners in liquid cough-treatment compositions. The limited portability of liquids limits the use of coolants in liquid compositions, and some high-intensity sweeteners, such as aspartame, are subject to degradation when heated.
In addition, the cooling agent itself can result in a burning effect if used at too high a level in the composition.
The cooling effect or sensation of cooling in the mouth is usually achieved using a polyol. The effect is caused by the negative heat of dissolution of such polyols in water, and is also linked to their rate of dissolution. Crystalline xylitol is in this respect particularly effective since it confers the most intense cooling sensation. Sorbitol and erythritol have slightly lower cooling effects than xylitol.
Xylitol, also called wood sugar or birch sugar, is a five-carbon sugar alcohol that can be used as a sugar substitute. It is derived from various types of cellulose products, such as wood, straw, cane pulp, seed hulls and shells. Xylitol is an odourless, sweet tasting granular solid (comprising crystalline, equi-dimensional particles). Xylitol has a sweetness level equivalent to sugar. The combination of a relatively large negative heat of solution and high solubility means that xylitol provides cooling sensation in the mouth that is said to be refreshing.
Sorbitol is a popular bulk sweetener found in numerous food products. In addition to providing sweetness, it is an excellent humectant and texturizing agent. Mannitol is a monosaccharide polyol. Both sorbitol and mannitol are generally stable and chemically unreactive.
The main disadvantage of xylitol is that it is an expensive ingredient. In addition, it is generally understood that a cooling effect will only be obtained when using crystalline xylitol. Accordingly, xylitol is often replaced with a less expensive sugarless polyol, such as sorbitol.